The Universe and Beyond, with Stephen Hawking

Join Neil deGrasse Tyson as he sits down with world-renowned physicist Stephen Hawking. We offer this episode in memory of Dr. Hawking's passing, and in celebration of his life. With co-host Matt Kirshen, astrophysicist Janna Levin, theoretical physicist Michio Kaku, and Bill Nye the Science Guy. NOTE: Watch this entire episode commercial-free here: https://www.startalkradio.net/all-access/the-universe-and-beyond-with-stephen-hawking/ Photo Credit: Brandon Royal.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Neil deGrasse Tyson?

  From the American Museum of Natural History in New York City, and beaming out across all of space and time, this is StarTalk, where science and pop culture collide. Welcome to the Hall of the Universe. I'm your host, Neil deGrasse Tyson, your personal astrophysicist, and tonight, we're featuring my interview with world-renowned physicist and cosmologist Stephen Hawking. Whoa.

• 0:35Neil deGrasse Tyson?

  I've picked his legendary brain on everything, from the Big Bang to the origins of the universe. So, let's do this.

• 0:46Neil deGrasse Tyson?

  So, my comedic co-host tonight is Matt Kirshen. Matt, all right, welcome back.

• 0:50Matt Kirshen?

  Thank you.

• 0:51Neil deGrasse Tyson?

  All right.

• 0:53Matt Kirshen?

  Nice to be back.

• 0:55Neil deGrasse Tyson?

  You co-host the science-based podcast Likely Science?

• 0:58Matt Kirshen?

  It's Probably Science.

• 0:59Neil deGrasse Tyson?

  Probably Science. I knew it had some statistical measure before it.

• 1:03Matt Kirshen?

  Every time, you come up with a different version, and I like it. I think it just starts cycling names.

• 1:07Neil deGrasse Tyson?

  Also joining me is my friend and colleague, theoretical physicist Janna Levin. Janet, welcome.

• 1:15Neil deGrasse Tyson?

  You're a professor at Barnard College of Columbia University, award-winning author, most recently of "Black Hole Blues" and other songs from outer space.

• 1:25Janna Levin?

  Nobody says it better than Neil.

• 1:28Neil deGrasse Tyson?

  "Black Hole Blues."

• 1:29Matt Kirshen?

  Do you get people asking to do your voicemail message?

• 1:33Neil deGrasse Tyson?

  Yeah, yes, but it gets worse than that. Yeah, yeah, yeah, yeah.

• 1:37Matt Kirshen?

  You're like, "I need to break up with my girlfriend, but I want it to sound good, so if you could just take this one."

• 1:42Neil deGrasse Tyson?

  "Hey, baby, I got other plans."

• 1:45Matt Kirshen?

  Oh, you take it from that, wouldn't you? You'd be like, "I'm sad at the end of my relationship, but that felt good."

• 1:51Neil deGrasse Tyson?

  So Janet, we'll be tapping your big brain on this because you're an expert. You're a theoretical physicist specializing in cosmology. And I know a little cosmology. We have some overlap there. Not as much as we need for this.

• 2:03Janna Levin?

  It's gonna be fun.

• 2:03Neil deGrasse Tyson?

  Situation.

• 2:04Janna Levin?

  Okay.

• 2:05Neil deGrasse Tyson?

  Stephen Hawking's been called one of our greatest minds of our generation, possibly of the century, and maybe ever. He's done groundbreaking work on black holes, relativity, cosmology. He has the mega bestselling book, A Brief History of Time. Sold 10 million copies. And it brought cosmology from the frontier of physics into people's living rooms. And now, there was a movie. A movie in 2014 called The Theory of Everything, starring Eddie Redmayne. And he won an Academy Award for Best Actor. So what more can you want in a career? I mean, man. So Hawking currently serves as Director of Research at the, what's the department?

• 2:45Janna Levin?

  Department of Applied Mathematics and Theoretical Physics.

• 2:48Neil deGrasse Tyson?

  That's why we have her. Excuse me. At the University of Cambridge. You worked there, is that right?

• 2:52Janna Levin?

  Yeah, I worked in that department for a few years, five years.

• 2:55Neil deGrasse Tyson?

  And you graduated from University of Cambridge, is that right?

• 2:57Matt Kirshen?

  I did, just about.

• 3:00Matt Kirshen?

  It was a close call, but I got there in the end.

• 3:02Neil deGrasse Tyson?

  So have you guys ever met Steve Hawking?

• 3:04Matt Kirshen?

  I saw him once, but it was at a talk he was giving, and I don't think that counts. That's like spotting an orca at SeaWorld.

• 3:11Matt Kirshen?

  But you know he's gonna be there.

• 3:14Neil deGrasse Tyson?

  So, in my interview with him before getting deep into physics, I just wanted to get to know him a little better as a person. We had met before, but we never really hung out like we did in this interview. So let's check out the first clip.

• 3:28Neil deGrasse Tyson?

  Professor Hawking, thanks for agreeing to be on StarTalk. And let me just start off with a first question. Perhaps the most pressing question to us all. What's your favorite food? For me, it's pizza. Actually, New York pizza. Oysters. Oysters? A little slippery for me, but that's cool. Okay, how about your favorite drink? Pims. Pims, ooh.

• 4:03Neil deGrasse Tyson?

  I like pina coladas myself, but if it's not alcoholic, I would do a milkshake. Okay, last question. Last question. What's your favorite equation? I know you've got one.

• 4:15Speaker 03

  The equation I discovered relating the entropy of a black hole to the area of its horizon. S equals A over 4.

• 4:25Neil deGrasse Tyson?

  How many people get to say their favorite equation is one they came up with?

• 4:30Neil deGrasse Tyson?

  That's badass.

• 4:39Neil deGrasse Tyson?

  What?

• 4:39Matt Kirshen?

  That's...

• 4:40Neil deGrasse Tyson?

  What?

• 4:40Matt Kirshen?

  I don't know, I think we just all got a glimpse of what it's like to be on a date with Neil.

• 4:45Matt Kirshen?

  Your favorite food, your favorite drink, now equation. And we'll get those results peer reviewed, and if they check out, then it becomes a relationship.

• 4:53Neil deGrasse Tyson?

  Then it's a relationship. So, just in case anyone had been living under a rock, Stephen Hawking has what we call Lou Gehrig's disease, ALS. So, and it's gradually paralyzed him over the decades. And right now, he communicates through twitches in his cheek. And these are read electronically. And he moves the cursor up and down on that screen, which we got a brief glimpse of. And he basically bangs out the spelling of words and ultimately sentences.

• 5:22Matt Kirshen?

  And then scientific papers.

• 5:24Neil deGrasse Tyson?

  That as well, yes, yes. So Janet, tell me about his favorite equation.

• 5:29Janna Levin?

  So, this is what's this incredibly stunning discovery that Hawking made. So, the entire idea of a black hole is that nothing can get out of it. That's the whole idea. It can't reflect light, it can't emit light. What falls in never comes out again. When you talk about the area of a black hole, what you're really describing is the region after which no information can ever escape, nothing.

• 5:48Neil deGrasse Tyson?

  So this is the surface region

• 5:50Janna Levin?

  Right.

• 5:51Neil deGrasse Tyson?

  surrounding the black hole.

• 5:52Janna Levin?

  Yes, and so there's nothing there. It's not a surface of any material kind. It's simply a boundary that separates what can come out and what can never come out again. And amazingly, Hawking realized, in some sense, which seems intuitive in retrospect, but it was very difficult that-

• 6:08Neil deGrasse Tyson?

  That's how you know it's really genius.

• 6:09Janna Levin?

  Yes, it is really genius.

• 6:10Neil deGrasse Tyson?

  It's obvious after somebody tells you.

• 6:11Janna Levin?

  If it can't emit anything, it certainly can't emit light or be illuminated in any way, but what he realized was that if it absorbs stuff, it must be taking entropy out of the other side of the boundary, right? Entropy being a measure of disorder or randomness, or in some sense, energy. And so if it takes entropy, there is a law of thermodynamics that says entropy always increases. You know, your room gets messier, not cleaner, without intervention, right? So disorder always increases. And so if it's taking entropy out of this side of the boundary, it must actually be producing its own entropy. And each time it takes something in, it gets a little bigger and has a little more entropy.

• 6:54Janna Levin?

  So in what form is this entropy is really the mystery. Then Hawking realized the black hole must be evaporating, it must actually be radiating at a temperature, like a hot object.

• 7:04Neil deGrasse Tyson?

  Okay, so that means a black hole is not entirely black.

• 7:07Janna Levin?

  Yeah. It would actually, from far away, if we were looking at a black hole in a very cold background, it would look to us like the black hole was actually emitting particles.

• 7:15Neil deGrasse Tyson?

  Had a temperature- Sorry. It was at a temperature radiating.

• 7:18Janna Levin?

  Yeah, it was radiating at a temperature, and that would explain this famous equation of Hawking.

• 7:24Neil deGrasse Tyson?

  So there are two major kinds of black holes we think of in astrophysics. One of them is the end state of a high-mass star. The sun will not become a black hole, but more massive stars can and do. And then we find black holes in the centers of galaxies with super-duper-high masses, and we call them supermassive black holes, because we tell it like it is. So I was always wondering what questions Stephen Hawking might have for my man, Isaac Newton. You know, Stephen Hawking is like, as the greatest physicist of modern times, and Isaac Newton, as the father of classical physics, I thought this would make an interesting exchange, if they could do such a thing. So I asked him, "Let's check it out."

• 8:05Neil deGrasse Tyson?

  You hold the same endowed chair that Isaac Newton did. I'm just wondering if we had some way to communicate through time with him? And tell him about what life is like today? Are there any questions, any problems you might want to hand him to solve?

• 8:23Speaker 03

  Is the solar system stable? And what happens to a star that cannot support itself against its own gravity?

• 8:32Neil deGrasse Tyson?

  Hmm, so you're thinking if Newton saw those questions, he might give us deeper insights into black holes? I'd be curious. Yeah, so what he did with that question was not what I thought he would do with it. What he did was, he asked questions of Isaac Newton at the boundary of where Isaac Newton left off in his own studies.

• 8:52Matt Kirshen?

  So stuff that he already knew the answer to?

• 8:54Neil deGrasse Tyson?

  No, that Hawking knew the answer to. Right, but I think he's testing, he wants to see...

• 8:59Janna Levin?

  How Isaac would do.

• 9:00Neil deGrasse Tyson?

  Yeah, how Isaac would do, because certain questions you might not even know to ask, even if you invented the theory yourself, Einstein didn't even think to take his equations to get a black hole out of them.

• 9:11Janna Levin?

  Right, the black hole was really discovered by somebody else.

• 9:13Neil deGrasse Tyson?

  But later on, with using his formula.

• 9:16Janna Levin?

  Yeah, within a year, yeah.

• 9:17Matt Kirshen?

  Wouldn't it be a crushing disappointment if Newton did come back and just wanted to know about Tinder? Like, "Tell me more about this dance-dance revolution."

• 9:26Neil deGrasse Tyson?

  Okay, of all things he might be curious about, Tinder would not be among them. All evidence shows that Isaac Newton died a virgin.

• 9:35Matt Kirshen?

  But he got a lot of science done, so that'd be a lesson to him.

• 9:38Neil deGrasse Tyson?

  Yeah, there you go.

• 9:39Matt Kirshen?

  Everyone out there getting it on. You could revolutionize the world.

• 9:45Neil deGrasse Tyson?

  So Janet, what question would you have for Isaac Newton, do you think?

• 9:47Janna Levin?

  Oh, that's an interesting question. Well, I think I would love to hear his response to Einstein's revelation. So Newton wrote down the stunning system of equations that describes not only how the apple falls from the tree, but how the moon stays in orbit around the Earth. I mean, that's a huge leap to think that...

• 10:05Neil deGrasse Tyson?

  To connect them.

• 10:06Janna Levin?

  To connect them. Celestial bodies' motion and the motion of stuff here on Earth. It was absolutely brilliant, but he knew that he didn't understand... How the earth was pulling on the apple without touching it. Or how the

• 10:18Neil deGrasse Tyson?

  Action at a distance.

• 10:19Janna Levin?

  Or how the earth was pulling on the moon without touching it. Action at a distance. And so Einstein has this beautiful intuition that what's actually happening is the masses are curving space and time and things are falling along the natural curves. I would love to hear if Newton was satisfied with that story. Or if he felt something was missing.

• 10:36Neil deGrasse Tyson?

  And do you think the leading question, what would happen if a star collapses? Do you think he could have landed on a black hole out of that?

• 10:41Janna Levin?

  There's no way not without modern physics. So if we look at the history of the discovery, so it was Einstein, even when he saw the mathematical solution for the black hole, did not believe nature would allow this to happen, as you well know. And after all, it is hard to crush stuff. You know, you want to crush an entire star, our sun, down to six kilometers to make a black hole. It'd fit in Manhattan, you know.

• 11:03Neil deGrasse Tyson?

  Yeah, if earth were a black hole, you would make it the size of a plum.

• 11:05Janna Levin?

  Yeah, the size of a plum. How do you do that? It's really not easy. I can't crush this cup. And so it was sensible for Einstein to think matter forces wouldn't allow it to happen.

• 11:15Matt Kirshen?

  Well, we even got a little, we got some of our scientists on the team to work out a case study for what would happen in a more localized situation.

• 11:21Neil deGrasse Tyson?

  You have scientists on the team?

• 11:22Matt Kirshen?

  We do, we've got scientists working behind the scenes here as well.

• 11:25Neil deGrasse Tyson?

  I didn't know you had that.

• 11:26Matt Kirshen?

  Yeah, so they worked out what would happen if Neil's stardom became just too much for you to handle. So you deactivate your Twitter account and here's what happens. We found, according to our calculations, there'll be a vacuum of celebrity selfies and Twitter fuses with flat-earthers. And eventually, the whole universe will collapse in on itself, so.

• 11:46Janna Levin?

  Wait, with Neil, it's the epicenter?

• 11:47Matt Kirshen?

  There is, so just be careful, be aware.

• 11:49Neil deGrasse Tyson?

  Oh, okay. Thanks for this warning, okay? You're a crack team of scientists on that one.

• 11:54Matt Kirshen?

  Yeah, don't blame me, they did all the work. It's been peer reviewed as well, they're very thorough on this show.

• 11:59Neil deGrasse Tyson?

  Well, you know, Hawking's, his discoveries and his personality have made him kind of like a pop culture icon. Everybody knows who he is and, and, and what he sounds like. And we've got some images, like.

• 12:12Neil deGrasse Tyson?

  Yeah, so this is one of his many animated appearances on The Simpsons. Here he is with Sheldon in The Big Bang Theory.

• 12:21Neil deGrasse Tyson?

  Oh.

• 12:23Neil deGrasse Tyson?

  Yeah, I was in this scene as well. Isn't that Bill Nye? Okay. So, we are floating heads. We've got Stephen Hawking, Bill Nye, George Takei, and me, and Futurama. So, Professor Hawking knows how to have some fun. He did that zero-g plane thing, you know, the zero-g thing?

• 12:44Matt Kirshen?

  I'm very aware of it.

• 12:44Neil deGrasse Tyson?

  I asked him about it. Let's check it out. Stephen, you've been in that zero-g airplane. I've always wanted to go. I just wondered what it felt like for you.

• 12:52Speaker 03

  It was wonderful to float weightless, free of my wheelchair.

• 12:58Speaker 03

  I could have gone on, and on, and on.

• 13:02Neil deGrasse Tyson?

  Hmm. Well, one day I'll try to do that, too. See what that's like. One problem for me, I get nauseous when I'm worried I'd throw up.

• 13:14Neil deGrasse Tyson?

  Yeah, you don't want to throw up in zero-g. You know, these zero-g airplanes, it's not that they go into orbit or go into space.

• 13:21Matt Kirshen?

  Yeah.

• 13:22Neil deGrasse Tyson?

  Yeah, what they do is, they go on an arc where you ascend as they, of course, move forward. Then there's a point where there's a precise trajectory down where the plane is basically in free fall. And while you're in free fall, you are weightless. And in fact, that's how Newton connected the free-falling apple to the orbiting moon. So, when you're in free fall, then you can, this happens. But you know what's even cool about those zero-g planes is they can do trajectories where they can simulate moon gravity or Mars gravity.

• 13:55Matt Kirshen?

  So they just do a shallow up for a while?

• 13:56Neil deGrasse Tyson?

  Yeah, they just do it in a way that it's not a full free fall. That they're slowly coming out of the free fall. And you can simulate any chosen gravity you want. It's very cool. So, coming up, more of my interview with world-renowned physicist Stephen Hawking when StarTalk returns.

• 14:16Neil deGrasse Tyson?

  Welcome back to StarTalk, right here at the American Museum of Natural History in New York City. We're featuring my interview with acclaimed physicist, Professor Stephen Hawking. And I asked him about one of the universe's biggest mysteries. Let's check it out. So Stephen, everyone wants to know, what was around before the Big Bang?

• 14:38Speaker 03

  Nothing was around before the Big Big Bang. According to Einstein's general theory of relativity, space and time together form a spacetime continuum or manifold which is not flat, but curved by the matter and energy in it. I adopt the Euclidean approach to quantum gravity to describe the beginning of the universe.

• 15:04Speaker 03

  In this, ordinary real time is replaced by imaginary time, which behaves like a fourth direction of space. In the Euclidean approach, the history of the universe in imaginary time is a four-dimensional curved surface, like the surface of the Earth, but with two more dimensions. Jim Hartle and I proposed a no-boundary condition. The boundary condition of the universe is that it has no boundary.

• 15:35Neil deGrasse Tyson?

  Okay.

• 15:36Speaker 03

  In order terms, the Euclidean spacetime is a closed surface without end, like the surface of the Earth. One can regard imaginary and real time as beginning at the South Pole, which is a smooth point of spacetime where the normal laws of physics hold. There is nothing south of the South Pole, so there was nothing around before the Big Bang.

• 16:03Matt Kirshen?

  The boundary condition of the universe is there is no boundary. Does everyone's minds just go clear at that moment? Like a zen monk has just enabled you to meditate truly for the first time.

• 16:15Neil deGrasse Tyson?

  So Jen, I'm there nodding like I'm following him.

• 16:17Janna Levin?

  He gave you a look at the end like, get it? Did you see that look he gave you?

• 16:20Neil deGrasse Tyson?

  I was like, I got maybe 20% of where he was going. So let's see if we can unpack this. What does he mean by imaginary time?

• 16:27Janna Levin?

  Well, imaginary time is really, it doesn't mean made up or invented time. It literally means you invent a new time parameter, which is, I'm gonna say it in math terms, the square root of minus one times the old time parameter. It's just a math.

• 16:41Neil deGrasse Tyson?

  And square root of minus one is the imaginary number.

• 16:43Janna Levin?

  It's an imaginary number. It doesn't mean that it's made up or invented. And it's just a mathematical trick.

• 16:46Neil deGrasse Tyson?

  It's a most unfortunate word for it.

• 16:48Janna Levin?

  It is.

• 16:49Neil deGrasse Tyson?

  That we gave it.

• 16:49Janna Levin?

  It is, but it is a pretty odd, it is a pretty odd little trick to do.

• 16:53Matt Kirshen?

  Well, technically, all numbers are imaginary, right? There's, you can't see a four.

• 16:56Janna Levin?

  I don't know, that looks like one microphone.

• 16:58Matt Kirshen?

  Yeah, but that, but you still need the word microphone. That's not like, that's not A1.

• 17:03Neil deGrasse Tyson?

  It's not A1. The one represents the microphone, yeah.

• 17:06Janna Levin?

  So in this mathematical trick, you're re-representing time as though it's actually space. That's ultimately what the mathematical trick does. So that when you do this in all of your mathematical equations, you literally couldn't tell what was time and what was space before, especially if you relabeled them to trick yourself. You know, like a little game of, what are they called?

• 17:24Neil deGrasse Tyson?

  Shell game, yeah.

• 17:25Janna Levin?

  So then what, what you're doing is you're imagining that instead of space and time, that you're just in space, but a four dimensional space. And that allows you to visualize certain aspects of the spacetime.

• 17:37Neil deGrasse Tyson?

  So what about then, there being nothing south of the South Pole?

• 17:41Janna Levin?

  Right, so then if time.

• 17:43Neil deGrasse Tyson?

  But first, we all agree, you can't go south.

• 17:45Janna Levin?

  Right, and there's nothing weird about that. You just go back again. So there is no, if you stay on the surface of the earth, you don't ask the question, what's south of the South Pole? You just realize, oh, that's just an ill-posed question and it's all completely compact. And so they would imagine an entire spacetime where as you move in time, this Euclidean time, you'd actually come looping back around again. It really is a hypothesis that is as yet unsubstantiated. We don't know that that's true.

• 18:08Neil deGrasse Tyson?

  She just said Hawking made a, was only a hypothesis.

• 18:10Matt Kirshen?

  Right.

• 18:11Janna Levin?

  It was only a hypothesis.

• 18:12Matt Kirshen?

  And he's not here to defend himself.

• 18:13Neil deGrasse Tyson?

  That's right. So it's time right now for that part of the show we call Cosmic Queries. Yes.

• 18:22Neil deGrasse Tyson?

  And we took your questions about the physics of space and time out there in the cosmos. And we've got cosmologist Jan Levin to make sure that anything I say is right and anything I don't know, you answer. You got that?

• 18:35Janna Levin?

  I'm on it.

• 18:36Neil deGrasse Tyson?

  All right, let's do this. Matt?

• 18:37Matt Kirshen?

  This one comes from Twitter from at the EMC Effect, appropriately named. If gravity bends light and the universe is curved, can we be sure we're not looking at our 13 billion year old rear end?

• 18:50Janna Levin?

  Ah, I love this question. It actually relates to what we were just talking about, which is if the universe is, has a shape where it is compact and completely connected, then we could be. So it's as though you walk, you leave New York City, you walk around the Earth and you come back to where you started. But in this case, light does it. So light leaves the Milky Way galaxy, it travels throughout the entire universe. And we're here some number of billions of years later and we're collecting light coming from behind us and we realize, oh, we're actually looking at an image of the Milky Way in our past. That is a completely possible scenario if the universe has this kind of connected property.

• 19:27Neil deGrasse Tyson?

  Except it's not actually your rear end. It's what your rear end would have been 13 billion years ago.

• 19:31Matt Kirshen?

  So there's every chance that in 13 billion years' time from now, they could be listening to a distant echo of this episode of StarTalk?

• 19:38Neil deGrasse Tyson?

  Yeah, yeah.

• 19:38Janna Levin?

  Or I love it, you know, it's Planet of the Apes. You leave in a rocket, you come to some distant planet and you realize the Statue of Liberty is buried in the sand, you came back to where you started.

• 19:48Janna Levin?

  Damn you all to hell.

• 19:50Neil deGrasse Tyson?

  God damn it, the hell you blew it up!

• 19:54Neil deGrasse Tyson?

  Okay, next question. Go.

• 19:56Matt Kirshen?

  From John Ron from Illinois. Do galaxies form around supermassive black holes? Or do supermassive black holes form in the center of galaxies?

• 20:06Neil deGrasse Tyson?

  Ooh, I haven't seen the latest on that, but consider that however massive these supermassive black holes are, the galaxy is vastly more massive than that. You can have like a million, even a billion times the mass of the sun in a supermassive black hole, but the mass of the galaxy is 400 billion times that. So that's just a point of fact. But at the very beginning of the universe, last I checked, I think the jury is still out on this.

• 20:33Janna Levin?

  Yeah, I think it's a really interesting astronomical question that we're answering right now. This is how, what astronomy is doing right now.

• 20:40Neil deGrasse Tyson?

  And we learned with the Hubble telescope that essentially every galaxy has a supermassive black hole in it. So that everybody's in the party on that. Okay, next one.

• 20:48Matt Kirshen?

  Oh, someone from my country, Vanessa Vima. Why is the speed of light around 300 million meters per second? That seems so random, why not faster or slower?

• 20:58Janna Levin?

  Oh, this is a great question.

• 20:59Neil deGrasse Tyson?

  Was he complaining that it's kind of a round number? Or?

• 21:03Matt Kirshen?

  She, I think it was like, why, why is that such, why that specific number?

• 21:07Janna Levin?

  We have no idea why any of the specific numbers that seem to be constants of the universe are what they are. And so the speed of light is actually comes out of electromagnetism. It's, it actually has to do with the strength of electricity and the strength of magnetism put together just makes this random number. So if those forces were weaker or stronger, the speed of light would be different. Similarly, if gravity were weaker or stronger, our entire universe would be different. And there are people who believe that we live in a multiverse in which these numbers are different in different manifestations of the universe.

• 21:38Neil deGrasse Tyson?

  And dare I say, in my latest book, there's a chapter called "On Earth As It Is In The Heavens." And it's a discussion of the laws of physics as measured on Earth and how, in fact, we came to discover that they apply across the universe and across time itself.

• 21:54Janna Levin?

  Yeah, if we look back to the early universe, there's no evidence that it's changed in our history.

• 21:58Neil deGrasse Tyson?

  Of the, of the laws of physics has changed.

• 22:00Matt Kirshen?

  So right from the moment the universe was created, the speed of light was exactly this amount?

• 22:04Neil deGrasse Tyson?

  Yes, from the earliest measurements that we could possibly make. Bam! Light, last question, go.

• 22:09Matt Kirshen?

  Final question from Derek Luterus from Oklahoma. How would a galactic empire keep a uniform standard of time?

• 22:18Janna Levin?

  This is on you, Neil. Let me just quickly pass this over.

• 22:23Neil deGrasse Tyson?

  I would just ask why, oh, an empire that is all coherent, right? Because if you didn't otherwise care, if it's too far away, what do you care?

• 22:32Matt Kirshen?

  Yeah, I'm guessing this question is sort of, all right, so on Earth, we have different time zones, but there's a universal time zone as well that we use. What's the galactic version of that?

• 22:39Neil deGrasse Tyson?

  Yeah, you couldn't, because the light travel time across a galaxy is 100,000 years. So there'd be no such thing as any meaningful simultaneity of what's going on, unless your communication channels happen through wormholes. And so, here's one side of the galaxy, here's the other side of the galaxy. That's 100,000 light-years to cross. And you create a wormhole connecting the two. And everybody's got a wormhole. And it'd be like a wormhole Skype connection. And then your signals go through the wormholes. Then you could do that.

• 23:09Matt Kirshen?

  All right.

• 23:10Neil deGrasse Tyson?

  Well, you agree?

• 23:11Janna Levin?

  Yeah, if you can keep a wormhole open, you can find a shortcut.

• 23:14Neil deGrasse Tyson?

  Yeah, yeah, there you go. You got that?

• 23:16Matt Kirshen?

  All right, so get on that, scientist.

• 23:19Neil deGrasse Tyson?

  Well, that's the end of Cosmic Queries. Up next, I ask Professor Hawking, is time travel possible when StarTalk returns?

• 23:33Neil deGrasse Tyson?

  Welcome back to StarTalk. We're featuring my interview with Professor Stephen Hawking, world-renowned physicist. And I've got with me physicist Michio Kaku. Michio!

• 23:46Neil deGrasse Tyson?

  A theoretical physicist, a professor at the City College of New York, New York Times bestselling author of The Physics of the Impossible, one of my favorite books of his, also The Physics of the Future and The Future of the Mind. So, Michio, you're kind of known for entertaining wild ideas in science fiction that could be based in actual fact. Does that characterize you accurately?

• 24:10Michio Kaku?

  I think it's better to say that I talk about science fact, which appears to look like science fiction, because people haven't kept up.

• 24:17Neil deGrasse Tyson?

  Ooh, very nice, very nice. So, I had to ask Professor Hawking a classic sci-fi question. All right, let's check it out.

• 24:29Neil deGrasse Tyson?

  So, Stephen, will we ever have the ability to travel backwards in time?

• 24:34Neil deGrasse Tyson?

  I'm thinking not, simply because if we ever did obtain that ability, we would have met somebody by now from the future.

• 24:42Speaker 03

  One might hope that we could warp spacetime so that one could go off in a rocket and come back in the past. But I have shown that this is not possible. The energy density is always non-negative.

• 24:57Neil deGrasse Tyson?

  Hmm, okay. Maybe that's a big if.

• 25:04Neil deGrasse Tyson?

  All we have to do is create negative energy density stuff. Then we'll all be able to travel backwards in time.

• 25:14Matt Kirshen?

  I've, uh...

• 25:16Neil deGrasse Tyson?

  What?

• 25:16Matt Kirshen?

  Well, I've done this show a few times now, and I think this is the one where I really do feel the dumbest. Like, uh, what is non-negative energy density?

• 25:25Neil deGrasse Tyson?

  Yeah, actually, I'm not even completely sure myself.

• 25:28Matt Kirshen?

  What is non-negative energy density? I feel like we saw...

• 25:31Neil deGrasse Tyson?

  Oh, yeah, Meacham, yeah, come on. It's got your name on it.

• 25:34Michio Kaku?

  On Star Trek, it's called dilithium crystals, which make warp-dry wormholes and time travel possible. For a physicist, it is negative matter and negative energy, things that fall up rather than falling down. Now, a black hole has positive energy, energy to rip the fabric of spacetime, but it's unstable. It collapses back on itself. You need negative energy or matter to keep it open. That's why Hawking made a very famous theorem showing that wormholes, showing that time machines, require negative energy to keep the black holes and things like this from collapsing again. It is anti-gravitational, repulsive,

• 26:19Michio Kaku?

  and that's what prevents the black hole from collapsing all the way.

• 26:23Neil deGrasse Tyson?

  Okay, so how are we gonna create negative energy?

• 26:25Michio Kaku?

  Negative energy already exists. If I have an advanced civilization, much more powerful than our civilization today, they could make large quantities of negative energy and perhaps go backwards in time and become masters of the universe. You could create wormholes to go across the galaxy, go backwards in time, witness the Big Bang.

• 26:48Neil deGrasse Tyson?

  That would then enable backwards time travel.

• 26:50Michio Kaku?

  That's right. In fact, Stephen Hawking himself has shown this theorem showing that the only way to go backwards in time is to have negative energy, energy below the zero of the ordinary vacuum.

• 27:03Matt Kirshen?

  So how do you avoid getting into a whole Martin McFly and mum situation?

• 27:08Michio Kaku?

  Because the river of time forks into two rivers into a multiverse. So when you go backwards in time to save Abraham Lincoln from being assassinated at the Ford Theater, it's someone else's Abraham Lincoln that you just saved. You cannot alter your own past. Quantum mechanics says that time itself can fission. Time itself can become a multiverse of parallel universes.

• 27:32Neil deGrasse Tyson?

  Right, didn't Hawking once come up with a backwards time travel conjecture? So that you don't have this Marty McFly problem?

• 27:40Janna Levin?

  Chronology protection conjecture.

• 27:42Neil deGrasse Tyson?

  And what does that protect?

• 27:43Janna Levin?

  It protects the order of causal events so that you are unable, even if there exists mathematically on paper the possibility to go back in time, you can't kill your mother before you were born because that would be inconsistent.

• 27:57Neil deGrasse Tyson?

  Okay, so Michio is gonna get around that by saying time forks.

• 28:01Michio Kaku?

  That's right. According to the quantum principle, time is constantly forking so that our universe, being a bubble that expands, can actually become a multiverse like in a soap bubble. So a soap bubble bath, think of lots of bubbles bifurcating, colliding with each other, and that's the Big Bang. The Big Bang is nothing but the collision or the fissioning of soap bubbles in a bubble bath called the landscape of the multiverse. This is now the dominant theory in quantum cosmology.

• 28:32Neil deGrasse Tyson?

  If time travel, it may not be possible unless we have this negative energy density stuff.

• 28:37Janna Levin?

  Well, this is something I've never seen.

• 28:38Michio Kaku?

  But showing that negative energy exists.

• 28:39Neil deGrasse Tyson?

  It may be possible for us all the day we harness

• 28:42Michio Kaku?

  That's right.

• 28:42Neil deGrasse Tyson?

  this negative energy stuff. But that is sometime in the future, at a point unknown. But what is true right now is that we have space travel, even if time travel is not available to us right now. So I asked Stephen Hawking, what is his sort of bold vision for humanity's future beyond Earth? In the form of space. Let's check it out. So Stephen, you've said publicly that you want us to be a multi-planet species. And who could argue that? I'm with you there. However, I have one mild rebuttal. Because you defend that argument by saying something bad could happen here on Earth. An asteroid, a runaway virus, rendering us all extinct.

• 29:27Neil deGrasse Tyson?

  And if we exist only on one planet, that's the end of the human species. I get that. But here's my mild rebuttal. Isn't it easier to deflect an asteroid? Easier to find a super serum that will combat any deadly virus? Than it is to terraform Mars and ship a billion people there?

• 29:49Speaker 03

  Collision with an asteroid is one of the least of the dangers we now face.

• 29:56Speaker 03

  The last collision was seventy million years ago. Nuclear war, climate change, and pollution are now much greater threats. Of course, it would be impossible to move the population of the Earth to a new planet, but if we can establish independent self-sustaining colonies in space, it would ensure the survival of the human race in the event of a disaster on Earth. Living Earth will also give us a new perspective and cause us to look outwards rather than inwards. It would also unite us to face the common challenge.

• 30:38Neil deGrasse Tyson?

  Whoa.

• 30:43Neil deGrasse Tyson?

  So Jan, are you ready to go to Mars for these reasons?

• 30:45Janna Levin?

  Yeah, I think, isn't it still a one-way ticket, though? Isn't that one of the problems? I mean, we could get to Mars with the technology we have now and the money we have now, but we can't get people home, so that's, you know...

• 30:57Neil deGrasse Tyson?

  Well, we actually interviewed somebody on StarTalk who had signed up for the one-way trip. And it was a little odd because, you know, he was all excited about it. And apparently, he's married, so I said, "What does your wife say about it?" And he said, "Oh, she encouraged it." And I'm thinking, "Uh, have you really looked at your situation?"

• 31:14Matt Kirshen?

  She's building her own rocket. She says if NASA doesn't get there, then she's gonna do it herself.

• 31:19Neil deGrasse Tyson?

  So Michio, are you a big fan of colonizing other planets?

• 31:22Michio Kaku?

  Yes, in fact, there's gonna be a traffic jam over Mars around 2030. Elon Musk, NASA with the SLS booster rocket, and now amazon.com. I mean, everyone's jumping in the game now to create booster rockets capable of taking us to Mars on a two-way trip. Amazon's the only one, by the way, that's going for same-day delivery.

• 31:44Neil deGrasse Tyson?

  Good one. Only if it's Amazon Prime, right, right, right. So, I think at a different point, Hawking had said that civilization only has 100 years left on Earth, which seemed a little pessimistic to me. And Jana?

• 31:59Janna Levin?

  Well, I mean, I don't think, I worry, I say this too much. I don't think we look like the most successful species that's ever walked the face of the Earth. I mean, dinosaurs were here for hundreds of millions of years. Like, we invented, you know, industrialization, sort of took over in the past couple hundred and we're already near threatening our own demise. So, it doesn't look great for us, to be honest.

• 32:21Michio Kaku?

  Ooh. I think if we don't blow ourselves up, we'll become what is called a Type 1 civilization in 100 years. That is, a planetary civilization. A Type 2 civilization is stellar, they control the power of an entire star, few thousand years into the future. Then Type 3 civilization is galactic, they control black holes, they control the energy of an entire galaxy. Now, on this scale, we are Type 0. We get our energy from dead plants, oil and coal. We don't even rate on this scale. But if we can make it to the next 100 years, if we can make it through it, we will become a Type 1 civilization, truly planetary. And that'll be the greatest transition in the history of the human race.

• 33:04Michio Kaku?

  From segmented nations that fight each other with fundamentalist ideologies, to a planetary civilization that is secular, scientific, multicultural, and at peace. If we can make it through the next 100 years, then we make it to Type 1.

• 33:21Matt Kirshen?

  Well, this is a perfect time for our game show, how we're not gonna make it through the next 100 years. So, we did a little survey of how the world will end. Neil, what do you think?

• 33:37Neil deGrasse Tyson?

  My money's on the zombie apocalypse.

• 33:38Matt Kirshen?

  Zombie apocalypse, let's see if it's up there.

• 33:41Neil deGrasse Tyson?

  No! Okay, all right.

• 33:44Matt Kirshen?

  Oh, shame on you, Neil. Jana?

• 33:46Janna Levin?

  Okay, let's do nuclear, nuclear holocaust.

• 33:49Matt Kirshen?

  All right, nuclear holocaust.

• 33:50Neil deGrasse Tyson?

  Nuclear war!

• 33:51Michio Kaku?

  Nuclear war was up there.

• 33:55Neil deGrasse Tyson?

  Mito!

• 33:56Janna Levin?

  And here we are.

• 33:57Michio Kaku?

  I wanna be the bad boy and say that we will survive, that humanity will struggle through, will squeak by, and we're not gonna end ourselves.

• 34:07Neil deGrasse Tyson?

  Ooh.

• 34:08Michio Kaku?

  Let's see.

• 34:09Neil deGrasse Tyson?

  You're wrong!

• 34:13Neil deGrasse Tyson?

  So Matt, let's see all the answers.

• 34:14Matt Kirshen?

  All right, let's see what we got, let's see what we missed.

• 34:16Janna Levin?

  I think AI is gonna be up there.

• 34:17Matt Kirshen?

  AI, I take...

• 34:18Janna Levin?

  Artificial superintelligence.

• 34:21Matt Kirshen?

  AI was up there. Good old fashioned non-nuclear war. I'm not sure that would end the world, but asteroid and climate change at number one.

• 34:28Neil deGrasse Tyson?

  Yeah, yeah. We agree that all of this is bad.

• 34:31Janna Levin?

  All of this is possible.

• 34:33Neil deGrasse Tyson?

  Well, up next, I asked physicist Stephen Hawking about the future of our minds when StarTalk returns.

• 34:47Neil deGrasse Tyson?

  Welcome back to StarTalk from the American Museum of Natural History. We're featuring my interview with famed physicist Stephen Hawking. Check it out. So Stephen, if we ever really developed the technology to upload your brain into some computer, providing life after death, or at least consciousness after death, would you be first to sign up for that?

• 35:13Speaker 03

  My body hardly works at all because I have motor neuron disease, otherwise known as ALS. So getting rid of it would be no loss and would spare me discomfort. Being more or less solely a brain, I could see the future unless I was terminated by someone switching off the computer or by a computer virus.

• 35:39Neil deGrasse Tyson?

  Whoa, I hadn't thought about that.

• 35:43Neil deGrasse Tyson?

  Right, if you're a computer, you're susceptible.

• 35:46Janna Levin?

  You could have copies.

• 35:47Neil deGrasse Tyson?

  You just make a backup of yourself.

• 35:48Janna Levin?

  Yeah, make a backup.

• 35:49Neil deGrasse Tyson?

  So, Misha, the title of your book, The Future of Mind: The Scientific Quest to Understand, Enhance, and Empower the Mind. When will uploading our brain become a reality?

• 35:59Michio Kaku?

  Well, just remember that...

• 36:00Neil deGrasse Tyson?

  If at all.

• 36:01Michio Kaku?

  Digital immortality is starting now.

• 36:04Neil deGrasse Tyson?

  So this is an example of what's going on here.

• 36:06Michio Kaku?

  That's right, telepathy, telekinesis, uploading memories, recording dreams. We can, quote, "do all of the above." This is no longer science fiction. You go to the physics laboratories and you can see how images can be extracted from the human brain. How it's possible now that we can upload memories in animals and record memories from animals because physics can now probe thoughts as they go ricocheting through the brain.

• 36:36Neil deGrasse Tyson?

  Is what you're describing the same thing as consciousness? Because if that's the case, then we can say it's not just our thoughts that live forever. It's our very identity, our self, our conscious self, that lives forever.

• 36:49Michio Kaku?

  Well, there is a theory that says the soul, the soul is information. It's a vast amount of information, but nonetheless, it's information that can be put into holographic form, such that even if you pass away, something there is, survives.

• 37:07Matt Kirshen?

  But theoretically, that is effectively immortality. Once you reach that point, that is you living forever.

• 37:13Michio Kaku?

  Why not have digital immortality? Wouldn't you want to talk to your great, great, great, great, great grandkids? Who want to meet their great, great, great, great ancestor?

• 37:20Matt Kirshen?

  It depends what they're like.

• 37:21Neil deGrasse Tyson?

  This gives you, this gives you movement throughout time and throughout space. So this is being godlike.

• 37:28Michio Kaku?

  Well, that's what we're talking about, transcending the human race.

• 37:31Neil deGrasse Tyson?

  Because I, I asked Stephen Hawking about his thoughts on the future of religion. Just, just to get his sense of this spirituality going forward. Let's check it out. So Stephen, religion has been around for thousands of years and it long predates science. And in spite of the effort of modern ardent atheists, religion persists. So do you have any sense of what religion will be in the future of civilization?

• 38:01Speaker 03

  Religion was an early attempt to answer the questions we all ask. Why are we here? Where did we come from? Nowadays, science provides better and more consistent answers. But people will always cling to religion because it gives comfort. And they do not trust or understand science.

• 38:25Neil deGrasse Tyson?

  Yeah, Stephen Hawking is imagining that any time you didn't understand something and ascribed it to deity, science would then fix that. For you. But there's the rest of what people use religion for. The spiritual fulfillment and the rest of this. And it's not obvious that science has solutions to that going forward.

• 38:45Janna Levin?

  But don't you feel a sort of surge of excitement?

• 38:49Neil deGrasse Tyson?

  All the time.

• 38:50Janna Levin?

  And the thrill and the connection to the universe? Just to know that even though we're stuck on this silly little rock, that we're able to know that much?

• 38:56Neil deGrasse Tyson?

  Oh, yeah.

• 38:56Janna Levin?

  That's stunning.

• 38:57Neil deGrasse Tyson?

  I'm deeply moved.

• 38:58Janna Levin?

  Yeah, it is. It is deeply moving. So this whole kind of notion that, oh, it leaves you feeling cold and sterile, that there is this scientific thinking is actually has been the opposite of my personal experience with it.

• 39:09Michio Kaku?

  Yeah, I think we're hardwired that way. Evolution has given us a brain to be receptive to awe, to receptive to beauty. And that's why there's a God gene. Because we are genetically programmed to believe in superstition. Because that's the way it has always been, even today.

• 39:23Janna Levin?

  Touch wood.

• 39:24Michio Kaku?

  Before science came along.

• 39:25Neil deGrasse Tyson?

  Touch wood.

• 39:28Neil deGrasse Tyson?

  Knock on wood. Knock on wood. Is it true? Well, coming up, the one and only Stephen Hawking offers some life lessons for us all. Next on StarTalk.

• 39:45Neil deGrasse Tyson?

  Welcome back to StarTalk from the American Museum of Natural History. And we're featuring my interview with legendary physicist Stephen Hawking. And I wanted to hear more about Stephen Hawking's perspective on life. And so I asked him, who's his favorite non-scientist? Check it out.

• 40:04Speaker 03

  A few years ago, I would have said Nelson Mandela.

• 40:09Speaker 03

  He brought a peaceful solution to a seemingly impossible situation. There is no one of his stature today.

• 40:20Speaker 03

  Certainly not Donald Trump.

• 40:27Neil deGrasse Tyson?

  Whoa.

• 40:30Janna Levin?

  Do you have an answer to this question?

• 40:32Neil deGrasse Tyson?

  Favorite non...

• 40:36Neil deGrasse Tyson?

  Yeah.

• 40:36Janna Levin?

  You're gonna get in trouble, whatever you say.

• 40:38Neil deGrasse Tyson?

  Yeah.

• 40:38Janna Levin?

  You're gonna have to go home.

• 40:41Neil deGrasse Tyson?

  No, my favorite... No, my wife is a scientist, so...

• 40:43Janna Levin?

  Oh, that's...

• 40:43Neil deGrasse Tyson?

  Yeah, she has a PhD in mathematical physics.

• 40:47Neil deGrasse Tyson?

  So there. Light Neil would marry a non-scientist.

• 40:52Neil deGrasse Tyson?

  Oh, okay. You know what I would say? Vincent van Gogh. His painting, The Starry Night, in 1889, is artwork that was given a name, not for what he drew in the foreground or the mid-ground. It was named for what appeared in the background. There's a village. He could have called it Sleepy Village, or Cypress Tree, or Rolling Hills. But no, the universe was speaking to him more loudly than his foreground. And out of that came the title, The Starry Night. And you look at that painting, it's obviously not what he saw, because the real universe doesn't look like that. But you know it is what he felt.

• 41:36Neil deGrasse Tyson?

  He drew what the universe felt like. And I am a fan of all the ways that artists can be touched by not only science in general, but the universe in particular.

• 41:51Neil deGrasse Tyson?

  This is my man, Vincent van Gogh.

• 41:57Neil deGrasse Tyson?

  Good, huh?

• 42:00Neil deGrasse Tyson?

  Before we wrap up this segment, and before we wrap up the show, I have a dispatch from my good friend, Bill Nye the Science Guy. And he's gonna give us his thoughts on the big ideas proposed by physicists like the great Stephen Hawking. Check it out.

• 42:17Bill Nye?

  Our curiosity brings us to places like this. The Griffith Observatory in Los Angeles, California. Here, we look through these telescopes and ponder the cosmos and our place within it. And it's one thing to think about the cosmos, but it's another thing to realize that the cosmos is different now than when I started talking. It's changing. I mean, we think of the cosmos in terms of space. We think of it in terms of time. But in astrophysics, we think of it in terms of spacetime. I mean, moving through space seems straightforward enough, but moving through time, that's a tricky one. It's been speculated that there are yet undescribed particles of time, tiny bits of time.

• 43:02Bill Nye?

  And if they turn out to be real, they will be discovered out there in the cosmos. So tonight, go outside and have a look. There's time. Back to you, Neil.

• 43:17Neil deGrasse Tyson?

  Bill, nice.

• 43:21Neil deGrasse Tyson?

  So, Mitro, I've not heard of this. Is this particles of time? Is this real?

• 43:25Michio Kaku?

  Well, you can look at it as gravitons.

• 43:28Matt Kirshen?

  So they are kind of to the force of gravity what photons are to electromagnetic force?

• 43:33Michio Kaku?

  Exactly. A photon is a particle of light. A graviton is a particle of gravity. And when the graviton becomes big enough, it becomes a universe, giving us a multiverse of universes.

• 43:44Neil deGrasse Tyson?

  So what you're saying is that what Bill might have been talking about as particles of time are just particles of spacetime?

• 43:51Michio Kaku?

  That's right.

• 43:51Neil deGrasse Tyson?

  Where space and time are wrapped together?

• 43:53Michio Kaku?

  That's right.

• 43:54Neil deGrasse Tyson?

  Oh, I see. Okay. So, in my final clip with Stephen Hawking, I asked him if he would just share with me some parting words of wisdom. Check it out.

• 44:06Neil deGrasse Tyson?

  So, over the course of your life, you've had a sort of unique perspective on science, on technology, endurance. If you sort of sum that together and offer some insight for us? Any lessons that we can take with us?

• 44:26Speaker 03

  We must all do the best we can in whatever situation we're in. Never give up.

• 44:34Neil deGrasse Tyson?

  Never give up.

• 44:37Neil deGrasse Tyson?

  Clearly, that advice applies to us all.

• 44:43Neil deGrasse Tyson?

  It's a privilege to spend this time with you. Thanks for your thoughts and your insights and being a source of inspiration to us all.

• 44:52Speaker 03

  Thank you.

• 45:02Neil deGrasse Tyson?

  How could you not just wonder what's going on inside this guy's head? I think our greatest gift as a species is not our body. We're not the fastest, we're not the strongest. Our body hardly distinguishes itself in any way in the animal kingdom.

• 45:24Neil deGrasse Tyson?

  Our greatest sort of gift in the tree of life is our mind. And perhaps no one knows that better than Stephen Hawking. And so much so that he does not take his mind for granted, enabling him to go places that we might never even dream of,

• 45:47Neil deGrasse Tyson?

  simply because he has power of mind where he has power from no other part of his body. So maybe it is we who are imprisoned,

• 46:02Neil deGrasse Tyson?

  thinking our body matters, when in fact, at the end of the day,

• 46:07Neil deGrasse Tyson?

  it's really all about your thoughts, all about your dreams, all about how we react to our life experience in this world and share it with others.

• 46:25Neil deGrasse Tyson?

  That is a cosmic perspective. You've been watching StarTalk. And I've been your host, Neil deGrasse Tyson, your personal astrophysicist.

• 46:38Neil deGrasse Tyson?

  I want to thank Matt, Jenna, and Nicho.

• 46:48Neil deGrasse Tyson?

  Thanks for being with us. We'll see you next time. As always, I bid you to keep looking up.